Range hood unit with fire safeguard fan control system

ABSTRACT

A range hood for use over a cook stove, which may be either ducted or ductless, and is provided with filters as required by its being ducted or ductless, respectively. An electric motor driven fan within the hood may be manually controlled, but additionally a safety circuit is provided to energize said fan motor automatically when cooking is being done even if said manual switch has not been actuated. Said safety circuit is also arranged automatically to shut off said fan motor, and if desired to energize a signal, in the event of a flash fire or the like. The automatic energization and de-energization of said fan motor is accomplished by means of self-resetting sensor-thermostats. The safety circuit does not interfere with fan speed control by means of said manual control.

nite States te Ferlise et al.

[4 1 Sept. 12, 1972 Primary ExaminerEclward J. MichaelAttorney-Melville, Strasser, Foster & Hoffman [72] Inventors: LouisFerlise; Ronald E. Duhamel, v

. both of Middletown, Ohio [57] ABSTRACT A range hood for use over acook stove, which may be [73] Asslgnee' gfil Corpommm ,Cmcmnat" eitherducted or ductless, and is provided with filters as required by itsbeing ducted or ductless, respective- [22] Filed: Sept. 17, 1970 ly. Anelectric motor driven fan within the hood may be manually controlled,but additionally a safety cir- [2!] Appl' 73121 cuit is provided toenergize said fan motor automativ cally when cooking is being done evenif said manual 52 US. Cl. ..9s/11s K Switch has not been actuated- SaidSafety circuit is also 51 Int. Cl. ..F23j 11/02 arranged automaticallyto Shut Off Said fan motor, and 58 Field of Search .Q ..9s/115 K- 236/11if desired energize Signal in the event a flash fire or the like. Theautomatic energization and deenergization of said fan motor isaccomplished by [.56] References Cited 1 means ofself-resettingsensor-thermostats. The safety UNIT N' circuit does notinterfere with fan speed control by 2,143,569 1./1939 f Nessell ..236/11X means 'ofsald maxim] control 2,971,452 2/1961 Graswich et al; ..98/115 K 3,055,285 9/1962 Gaylord ..98/1l5 K 6 Claims, 4 Drawing Figur' es4:1 I42. ii I (5 ZZZ; 11A

23 l Q 25 'l 1161 L I 2 11a RANGE HOOD UNIT WITH FIRE SAFEGUARD FANmeans a box-like ventilating'shield (open at the bot- 'tom), usuallyfabricated from 'shee'tsteel, which is designed to be installed in ahorizontal position, spaced above 'a cooking stove, for the purpose ofremoving the heated, air, water vapor or steam, smoke particles, greaseparticles and volatile fat vapors, as well as the odors that result frommany food cooking operations.

The range hood "also serves topresent staining and heat discoloration ofthe ceiling above, andthe wall surface behind and above the stove,caused by smoke and greaseparticlesthat are produced in cooking, fry-,ing and broilingof food-on the top burners.

g j An essential component of any range hood is a fan or blower, powered:by .a small electric motor, whichprovides an induced draft of airmovementto draw the heated-air'and other volatile products of thecooking operation from the space above the burners into the hood. Thisremoval of the heated air and other volatiles prevents theiraccumulation in the stove area and thereby results in cooler comfortconditions for the housewife. The blower motor is usually controlled bya manually operated off-and-on switch, having either one on" position,or a low and a high speed on position, or low, medium, andhigh-;on.positions.

There are two basic types of range hoods for home kitchens ducted andductless. The ducted hood is provided with ari outlet orifice onthedischarge side of the blower which is connected to aduct that dischargesthe heated air and other volatile and airborne products that are carriedin the airstream to the air outside the kitchen. When the cooking rangeis in a kitchen location that does not afford convenient access to awall in which a duct to discharge the heated air outside thebuilding'may be installed, theductless type of range hood can be used.With the ductless hood the heated air from the cooking operation isfirst thoroughly filtered to remove grease, smoke and fine foodparticles and to absorb cooking odors, and is then returned to the upperair of the room through a vent at the top of the hood, overhead and awayfrom the cooking area. The main disadvantage of the ductless range hoodas compared with a ducted hood is that the heated air and steam fromfood cooking are not removed from the kitchen, and consequently thecooling effect provided by the ducted hood is not obtained.

' A ducted range hood could be operated without a filter, since theheated air, steam and other volatiles are discharged outside thebuilding. However, such operation is unsatisfactory because grease andfood particles tend to collect on the fan blades and in the dischargeduct which then becomes unsanitary and also involves a fire hazard. Theducted hood therefore requires a grease filter for satisfactory, safeoperation. The grease filter is an open-mesh, framed panel, installedwithin the rangehood below the blower, so that all the heated air drawninto the hood by the fan first passes through the filter which collectsvirtually all of the grease and other food particles or spattercarriedin the airstream. The grease filter is usually constructed from anon-corrodible metal, such as aluminum, usually in the form of coarseexpanded mesh made from thin sheet aluminum. This expanded mesh is ofopen structure so as not to restrict appreciably the air flow induced bythe fan. "Also, it is preferably coated or chemically treated so as toincrease its ability to adhere toand retain grease and other foodparticles in the air stream and to improve ease of cleaning the filter.An especially effective coating material for an aluminum mesh greasefilter is Teflon-S (a polyfluorocarbon product of .the DuPont Company);but various other synthetic greaseresistant coating materials maybe-used lolyrnerized fluorocarbons, such as polytetrafluoroethylene andfluorinated ethylene-propylene, are the preferred coating compositions,due to their chemical inertness,

resiliency, resistance to moisture and steam, wide range of servicetemperatures, heat resistance up to 500 F. without carbonization, andresistance to :embritt'lement; Because substantialquantities of greaseaccumulate in the, filter interstices from continued use of therange-hood, the framed filter panel isinstalled .so .as' to be easilyremovable for cleaningffhegrease' accumulation is 'easilyremoved byflightagitation of the filter 4 mesh with a detergent solution and thefilter panel,

after drying, may be re-installed in the hood for another period ofservice.

The ductless type range hood also requires a grease filter ofthesamekind as used with the ducted hood. In addition, the ductless hoodis usually provided with a granulated, activated charcoal filter toabsorb cooking odors; it may also have a filter of spun glass fiber thatmay be chemically treated or. coated to enable it to absorb smokeparticles and also any fine grease particles that may not have beentrapped by'the aluminum mash grease filter. The activated charcoalfilter and the glass fiber filter are inexpensive and are intended to bereplaced-after a period of use, before they become clogged andineffective.

It is obvious that there is a fire safety hazard associated with thecooking of food over'an open gas flame such as the burner of a gasrange, and also to a lesser degree with electrical resistance burners.This hazard is especially present in the frying of fat meat such asbacon, the broiling of steaks, deep fat frying, etc. due to the highcombustibility ,of fats, both of 7 animal and vegetable origin. Manydisastrous home fires havestarted in the kitchen with a grease tire onthe cooking stove as the cause.

The ducted range hood is a very desirable adjunct to a cooking rangebecause it removes theheated air, steam, smoke, volatile fat vapors andgrease particles from the cooking area, thereby improving the comfortconditions in the kitchen. When the cooking operation is properlymanaged by the housewife, thehood does not increase the natural hazardsinvolved in cooking food. However, the range hoods previously availablehave depended on manual setting of the switch for starting and forcontrol of the fan blower speed, and thus require continuous attentionto the cooking operation. The previous range hoods have lacked anyautomatic fire safeguard devices.

It is evident that if the blower fan in the range hood is not startedwhen cooking begins, the grease particles and fat vapors produced willtend to accumulate in the heated air above the burners, which may resultin a flash fire. Therefore, the blower should always be in operationwhen cooking is being done, otherwise the range hood cannot perform thefunction for which it is intended. On the other hand, if a flash fireoccurs in the cooking area and the blower is in operation, it will drawthe flames into the hood and into the discharge duct where there may besome grease accumulation if the grease filter has been overloaded andnot cleaned as often as necessary. Such conditions may result in aserious fire in the duct and ignite adjacent combustible structuralmaterials. In any event, such 'a fire would do extensive damage to therange hood itself. Study of the various factors involved clearlyindicated that to prevent such an occurrence, the range hood must beequipped with an independent, automatic, fire safeguard system. whichwill insure that the blower operates when cooking is being done, but isshut off if and when a flash fire occurs.

BRIEF SUMMARY OF THE INVENTION The chief purpose of this invention is toprovide a prefabricated range hood unit that has greatly improved firesafety as compared with any range hood previously available, such thatthe cooking operation may be left unattended for a reasonable timewithout thereby appreciably increasing the fire hazard.

A further object is to provide the range hood with an auxiliaryautomatic, thermostatically controlled system for operation of theblower fan, such that when the temperature of air in the space above theburners rises to a point substantially above normal ambient temperature,say 140 F., the fan will start, and remove the heated air and othervolatile products of the cooking operation, even if the housewifeforgets to start the blower when the burners are first lighted.

Another object is to include in the automatic control system foroperation of the blower fan a sensor-thermostat which will stop the fanmotor and blower if the temperature of the air above the burners becomesexcessively high, say 240 F and which will at the same time actuate anaudible alarm such as a buzzer. Such a high temperature in the cookingspace usually is the result of a flash fire involving fat or grease.

A general object of the invention is to provide the range hood unit witha dual electrical system for control of the blower fan operation. Theprimary system is manually controlled by the housewife; an auxiliary,interconnected automatic system is controlled by sensorthermostats,which are set for selected temperatures to insure safe operation of theblower if the housewife is absent or inattentive, and if excessivelyhigh temperatures or a flash fire occur. Thus there is provided aneffective fire safeguard for the unit.

An incidental purpose is so to arrange the electrical circuitry of thedual blower fan control system that the auxiliary automatic system doesnot interfere with manual control of the fan speeds when that isdesired.

A further purpose is to provide the auxiliary automatic fan controlsystem with sensor-thermostats which, after the high temperaturethermostat has been actuated and has shut off the fan blower motor, willreset the system for continued safeguard operation when thetemperaturehas returned to the normal operating range below 200 F.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of acomplete assembled range hood unit embodying the features of thisinvention, showing the control panel for the blower fan and lights.

FIG. 2 is a cross sectional view of the range hood taken from front toback, showing the locations of motor, fan, filters, duct orifice, andthe spacing of the hood above the cooking stove top burners.

FIG. 3 is a view of the range hood from below, with the grease filterremoved, showing locations of the sensor-thermostats for F. and 240 F.automatic control of the blower fan operation, in relation to the blowerintake, fan and motor.

FIG. 4 is a schematic representation of the complete electrical wiringdiagram for the range hood unit of this invention showing the electricalconnections for the fan motor, themanual control solid statevariable-speed fan switch, the senso-thermostats for 140 and 240 F chokecoil, alarm buzzer, etc.

DETAILED DESCRIPTION OF THE INVENTION This invention will be describedas embodied in a range hood unit, either ducted or ductless, having agrease filter, and constructed with the arrangement of the parts asillustrated in FIG. 1, FIG. 2, and FIG. 3. It is to be understood,however, that the dimensions, arrangement and assembly of the partsshown in this typical example could be changed in various ways, or therange hood could have multiple filters, and the concept of the inventionwould still be effective as a tire safeguard for the range hood. Therange hood of the typical example of this invention is 36 inches long,19 inches wide from front to back, and 6 inches maximum depth frombottom to top and is adapted for use with a 36 inch domestic range.

In FIG. 1 the range hood is shown as comprising a prefabricated sheetmetal box-like structure open at the bottom, having a top 10a, 10b, andsides 11a and 11b (FIG. 3), a back 12 (FIG. 3) and a front panel 13. Thenumeral 14 indicates a knock-out panel for attachment of a duct adapter15 (FIG. 2). A similar knock-out panel is provided in the back wall 12.If the hood is to be ductless, the knock-out panels are left intact, anda vent grille is provided as shown in broken lines at 16. On the frontpanel are provided a pilot light 17, an on-off light switch 18, and asolid state fan speed control switch 19.

As best seen in FIG. 2, a grease filter 20 is provided, and it will beunderstood that a smoke filter and an odor filter may also be providedimmediately adjacent the grease filter 20, between the latter and theblower. The location of the hood with respect to the stove 21 and itsburners 22 is shown in this Figure. The bottom of the hood is suitablyspaced about 18 inches to 24 inches above the tops of the burners, foreffective performance of its functions.

FIGS. 2 and 3 show the location of the various components within thehood. An electric motor 23 is mounted on a bracket support 24, anddrives the fan 25. A volute housing 26 surrounds the fan 25 to directthe air to the duct adapters .15. It will be clear that only oneknockoout panel and one duct adapter will be used, depending on whetherthe ducting is to be upward or to the rear. The two adapters shown inbroken lines in FIG. 2 are used alternatively. Of course if the hood isto be ductless, the position of the volute 26 must be reversed as shownat 26a to blow the air out through the vent grille 16 provided for aductless hood.

At the front portion of the hood, one or more lights are provided as at27,and these are actuated by the onoff switch 18.

A 140 F. sensor-thermostat is located at 28, so as to be actuated byheated air rising from the burners. The

240 F. sensor-thermostat is shown at 29, within the exposed surface ofthe 140 F. sensor-thermostat 28. If

thefan motor has notibeen started the temperature will continue torise-due to the trapping of the heated air below and inside the hood.When the temperature at the sensor surface reaches 140 F. the thermostat(normally open) is actuated and closes the auxiliary power circuit tothe fan motor which then operates the fan at low speed. The timeinterval before the sensor-thermostat is actuated will vary somewhat,depending upon the number of burners that are lighted and whether theburners are, operating at highor'low heat, but under average cookingconditions the sensor-thermostat will start the fan motor in about 3minutes.

'The fan will continue to operate and ventilate the space above theburners while the air temperature remains in the normal cookingtemperature range of about 140 200 F.; but when the burners are 'shutoff and the air temperature at the sensor surface falls below about 125F. the bimetal thermostat disc will return to its normal open-position.This breaks the auxiliary electrical power circuit, stops the fan motor,and automatically re-sets the sensor-thermostat for its next exposure tocooking temperatures. The housewife thus can do many normal cookingoperations without using the manually controlled fan speed switch. If ahigher fan speed is desired this is provided by a suitable manualsetting of the fan speed switch 19, which is not affected by theauxiliary safeguard fan control.

If a flash fire occurs in the cooking area, due to combustible fatvapors, spatter or spills being ignited by the burner flame or heat, thehot air and flame will be drawn upwardly by the air stream toward thefan intake of the range hood. There the flame or high temperature airwill come into direct contact with the sensor surface of the 240 F.thermostat 29 which is mounted with the sensor exposed on the innersurface of the volute, as shown in FIG. 3. The 240 F. sensor thermostatis normally closed, but when exposed to this temperature by the flame orheat it is actuated to open the electrical contact and break the circuitto the fan motor. This thermostatic action also energizes the electricalcircuit to the audible warning signal 30 at the same time that the fanis stopped. In the range hood of the typical example, above described, abuzzer is used as the warning device, but other signals such as a bell,horn, or flashing light could be used.

After the grease fire has been extinguished and the air temperature onthe surface of the240 F. sensorthermostat 29 at the fan intake hasdropped below about 200 F. the bimetal thermostat will return to itsnormal closed position and restore the electrical circuit to the fanmotor. It should be pointed out that the 240 F. sensor-thermostat willoperate to stop the fan motor when the range hood is being used eitherwith the manually operated solid state speed control switch or with gthe auxiliary, thermostatically controlled safeguard fan system. Thus,an effective safeguard against an extensive fire in the range hood, ductor adjacent combustible structural materials is provided.

While any suitable thermostatic devices may be used, disc thermostatshave been found eminently suitable for these purposes. These devicesinclude a bimetal disc which responds to the specific temperature forwhich his calibrated, within a small plus or minus tolerance. Thethermostat may be constructed so as to be either open or closed atnormal temperatures and will then make or break the electrical contactwhen the design temperature is reached.,The bimetal-disc functions bothas the thermostat and as the temperature sensor and may be eitherexposed directly to the air stream or enclosed with a metal cap toshieldthe sensor face from accumulations of dust, moisture, or grease. Thecontact action of the bimetal disc in opening or closing the electricalcircuit is positive as the disc snaps through" at the calibratedtemperature. The moving parts are completely enclosed in a dust-freemetal chamber.

The sensor-thermostats used in the range hood of the typical example areof the disc thermostat type and are provided with protective metal caps.Their temperature response tolerances are plus or minus 6 F. for boththe 140 F. thermostat and the 240 F. thermostat. The

140 F. thermostat opens the electrical contact and resets itself whenthe air temperature drops to F., plus or minus 5 F. The 240 F.thermostat closes the electrical contact and re-sets itself when the airtemperature drops to 200 F., plus or minus 8 F.

These thermostats have been tested and approved and are listed byUnderwriters Laboratories, lnc. for use in temperature control withventilating fans.

Reference to the schematic wiring diagram of FIG. 4 shows that theprimary fan control circuit is provided with a speed control switch 19.This could be a conventional one-speed, two-speed or three-speed switch,but the preferred device for this control is a solid state speed controlswitch which provides infinitely variable speed settings between the lowand high speed limits of the fan motor. Whatever the nature of thisswitch, when it is in operation it over-rides the auxiliary automaticfan speed control and the F. sensor-thermostat control is inoperative.The electrical system therefore provides dual controls for the fanoperationa primary, manually controlled variable speed system and anauxiliary, thermostat-controlled, automatic safeguard system neither ofwhich interferes with the other performing its intended function.

Prefabricated domestic range hood units generally are made in lengthsfrom 24 inches to 48 inches, for use with cooking ranges of varioussizes, and the width from back to front normally is from 16 inches to 24inches so as to enable the hood to ventilate the heated air and cookingfumes from the front burners. The maximum depth of the hood, from bottomto top, is usually from inches to about 8 inches. Range hoods are madein various shapes, partly for the sake of more attractive appearance,but they usually taper in depth from back to front for more efficientremoval of the heated air by the fan, as shown in FIGS. 1, 2 and 3.

An important advantage of the dual control system for operation of thefan motor is that in the event of a failure of the primary manual speedcontrol, such as might result from the solid state speed switch becomingdefective or its electrical circuit being damaged, the range hood willcontinue to operate with the auxiliary automatic safeguard fan motorcontrol system. In fact, the range hood could be used for many yearswithout ever operating the manual fan speed switch, but of course onlyat the low fan speed provided by the safeguard control circuit.

It is obvious that the concept of this invention is adaptable toprefabricated domestic range hood units of varying sizes and shapes, toprovide a thermostatically actuated fire safeguard system for theoperation of the ventilating fan. Therefore no limitations on dimensionsor shape of the novel range hood unit have been included in thefollowing claims which define the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A range hood unit for installation above a cooking stove to ventilatethe heated air, steam and volatile products resulting from the cookingof food, comprismg a. an electric-motor-driven fan having an air intakeand an exhaust opening, and a grease filter positioned in said airintake opening,

b. a first sensor-thermostat disposed within said hood and operative atabout 140 F.,

c. a second sensor-thermostat disposed at the said intake opening andoperative at about 240 F.,

d. and an electric circuit including said fan motor and said first andsecond-thermostats, arranged to energize said fan motor when thetemperature immediately below said hood reaches about 140 F., and tode-energize said fan motor if the temperature of the air at the saidintake opening reaches about 240 F.,

e. whereby said fan operates automatically when cooking is being done,but is shut off automatically in the event of a flash fire or the likein the cooking area.

2. The structure of claim 1, including a warning signal element in saidcircuit arranged to be energized upon actuation of said secondsensor-thermostat.

3. A range hood unit for installation above a cooking stove to ventilatethe heated air, steam and volatile products resulting from the cookingof food, comprismg a. an electric-motor-driven fan, having an air intakeand an exhaust opening, and a grease filter positioned in said airintake opening,

b. a primary power circuit including said motor and a manually operatedspeed control switch for said motor, c. an interconnected auxiliarysafety power circuit including said motor and a first sensor-thermostatoperative at about l40 F d. said auxiliary circuit including also asecond sensor-thermostat operative at about 240 F.,

e. said first sensor-thermostat being arranged to energize said motorwhen the temperature of the air immediately below said hood reachesabout 140 F. if said manually operated switch is in the off position,

f. and said second sensor-thermostat being arranged to de-energize saidmotor if the temperature at said fan intake opening reaches about 240 Fregardless of the position of said manually operated switch or theaction of said first sensor-thermostat,

g. whereby said fan may be controlled manually, but will operateautomatically when cooking is being done even if said manually operatedswitch is off, and will be shut off automatically in the event of aflash fire or the like.

4. The structure of claim 3, wherein said exhaust opening is arranged tobe connected to an exhaust duct, wherein said manually operated speedcontrol switch is a solid state electronic switch having infinitelyvariable settings between its low and high speed limits, and whereinsaid auxiliary circuit also includes a warning signal element arrangedto be actuated by said second sensor-thermostat.

5. The structure of claim 3, wherein said hood is provided with a ventorifice connected to said exhaust opening, through which air is returnedto the room, a coated spun glass fiber filter, and an activated charcoalfilter in said air intake opening to remove smoke, grease and food odorsfrom the air before returning it to the room; wherein said manuallyoperated switch is a solid state electronic switch having infinitelyvariable settings between its low and high speed limits, and whereinsaid auxiliary circuit includes also a warning signal element arrangedto be actuated by said second sensor-thermostat.

6. The structure of claim 1, wherein said sensor-thermostats are of theself-resetting type, said first one resetting itself at about F.,andsaid second one at about 200 F.

1. A range hood unit for installation above a cooking stove to ventilatethe heated air, steam and volatile products resulting from the cookingof food, comprising a. an electric-motor-driven fan having an air intakeand an exhaust opening, and a grease filter positioned in said airintake opening, b. a first sensor-thermostat disposed within said hoodand operative at about 140* F., c. a second sensor-thermostat disposedat the said intake opening and operative at about 240* F., d. and anelectric circuit including said fan motor and said first andsecond-thermostats, arranged to energize said fan motor when thetemperature immediately below said hood reaches about 140* F., and tode-energize said fan motor if the temperature of the air at the saidintake opening reaches about 240* F., e. whereby said fan operatesautomatically when cooking is being done, but is shut off automaticallyin the event of a flash fire or the like in the cooking area.
 2. Thestructure of claim 1, including a warning signal element in said circuitarranged to be energized upon actuation of said secondsensor-thermostat.
 3. A range hood unit for installation above a cookingstove to ventilate the heated air, steam and volatile products resultingfrom the cooking of food, comprising a. an electric-motor-driven fan,having an air intake and an exhaust opening, and a grease filterpositioned in said air intake opening, b. a primary power circuitincluding said motor and a manually operated speed control switch forsaid motor, c. an interconnected auxiliary safety power circuitincluding said motor and a first sensor-thermostat operative at about140* F., d. said auxiliary circuit including also a secondsensor-thermostat operative at about 240* F., e. said firstsensor-thermostat being arranged to energize said motor when thetemperature of the air immediately below said hood reaches about 140* F.if said manually operated switch is in the off position, f. and saidsecond sensor-thermostat being arranged to de-energize said motor if thetemperature at said fan intake opening reaches about 240* F., regardlessof the position of said manually operated switch or the action of saidfirst sensor-thermostat, g. whereby said fan may be controlled manually,but will operate automatically when cooking is being done even if saidmanually operated switch is off, and will be shut off automatically inthe event of a flash fire or the like.
 4. The structure of claim 3,wherein said exhaust opening is arranged to be connected to an exhaustduct, wherein said manually operated speed control switch is a solidstate electronic switch having infinitely variable settings between itslow and high speed limits, and wherein said auxiliary circuit alsoincludes a warning signal element arranged to be actuated by said secondsensor-thermostat.
 5. The structure of claim 3, wherein said hood isprovided with a vent orifice connected to said exhaust opening, throughwhich air is returned to the room, a coated spun glass fiber filter, andan activated charcoal filter in said air intake opening to remove smoke,grease and food odors from the air before returning it to the room;wherein said manually operated switch is a solid state electronic switchhaving infinitely variable settings between its low and high speedlimits, and wherein said auxiliary circuit includes also a warningsignal element arranged to be actuated by said second sensor-thermostat.6. The structure of claim 1, wherein said sensor-thermostats are of theself-resetting type, said first one resetting itself at about 125* F.,and said second one at about 200* F.